1. X-Ray Spectroscopy in Astrophysics
Luigi Piro
Istituto Astrofisica Spaziale Fisica Cosmica, Roma
INAF

2. Summary
X-ray spectroscopy, the present instrumentation (CCD, gratings)
Opening a new window in Cosmology and Extreme physics
Enabling technology: TES microcalorimeters
Future missions: Xenia, IXO

3. X-ray spectroscopy in Astrophysics
Cryogenic microcalorimeters (T=100 mK) with high spectral resolution open a new observational window in Astrophysics and Cosmology.
Example of astrophysical plasma (107K) observed with:
* TES microcalorimeters (DE=2 eV, IXO, Xenia, DIOS)
*Si-base microcalorimeters (DE=6-8 eV: ASTRO-H)
*CCD (DE=100 eV:XMM)

4. Science Drivers
What are the fundamental physical laws of the Universe?
Matter under extreme conditions
How did the Universe originate and what is it made of?
The early Universe
The Universe taking shape
The evolving violent Universe

5. Structure Formation HOW ? z 10 1
Most of the baryon of the Universe are locked in large scale, low density structures visible only in X-rays z
High resolution spectroscopy and spatial resolution, wide field in emission 10 1
GRB as cosmological beacons: fast reaction, high res. absorption spectroscopy
Structure size
Stars
Galaxies
Clusters
Filaments

6. XENIA Cosmic chemical evolution of baryons
Undergoing US Decadal Survey 2010
As Medium Size Mission
International consortium of Institutes from US, Eu, Japan

7. XENIA: Mission and Payload
HARI: High Angular Resolution Imager
keV CCD
Field=1.4° ang.res=10” constant
Low bkg: LEO
equatorial
Autonomous fast pointing in 60 s
2 tons
TRL4
Decadal Survey
medium size
CRIS: Cryogenic Imaging Spectrometer
0.1-3 keV TES DE<2.5eV
Field=1.0° ang.res=3’
TED: Transient Event Detector
¼ of the sky, 3’ localization
8-200 keV

8. Tomography of the Universe: the X-ray forest from the Cosmic Web with GRBs
From 150 GRBs with afterglow Fluence> cgs
~200s OVII-OVIII filaments in 5 years

9. 3D mapping of the Cosmic Web
Model, Dz=0.01
Detected, OVII+OVIII in emission, 5 s, 1 Ms
4°x4°
Pixel size is 3 arcmin
>100 detecttions at five sigmas in the lines
Down to overdensities of 100

10. GRBs as cosmological probes
GB090423: z=8.2 !
GRBs as cosmological probes
About 90% have a X-ray afterglow, 20-40% are dark
High z events are dark (Lya forest absorption at z>6)
X-ray redshift
Observing a mid-bright GRB afterglow with a fast (min.) pointing XENIA yields 106 X-ray photons, and 103 cts in 1 eV resolution bin
Out of 400 =>Golden sample of >250 afterglows with high res. X-ray spectra: redshift, metals in host-galaxy and close environment from local to high-z universe

11. Narrow abs lines from ISM in our own host galaxy
Bright galactic binary ( ) observed with Chandra grating (Yao and Wand 2006)

12. Metal and ISM evolution with GRB
Metal enrichment in the environment of massive stars upto z>6
ISM of the host galaxy, kinematical studies of the outflows
Resonant absorption lines from GRB host galaxy at z=1
X-ray metal edges from a GRB nearby environment at z=7

13. IXO International X-ray Observatory
Undergoing Dedadal Survey 2010 and
ESA Cosmic Vision
As Large Mission
International consortium of Institutes
from US, Eu, Japan

14. IXO 5 year life; 10 years on consumables
Deployable Metering Structure w/Shroud
Flight Mirror Assembly
X-ray Microcalorimeter Spectrometer
Wide Field X-ray Imager
Hard X-ray Imager
X-ray Grating Spectrometer
High Time Resolution
X-ray Polarimeter
Spacecraft Bus Module
Atlas V 551 Medium Composite Fairing
5 year life; 10 years on consumables

15. Comparing IXO to Existing Missions
The improvement of IXO relative to current X-ray missions is equivalent to a transition from the 200 inch Palomar telescope to a 20m telescope, and at the same time shifting from spectral band imaging to an integral field spectrograph

16. Science Drivers Matter under extreme conditions:
Supermassive Black Hole Growth
Matter Orbiting a Black Hole
Neutron Star Equation of State
Formation of Structures:
Nature of Dark Matter and Dark Energy
Cosmic Feedback
Missing Baryons
Observatory Science (Life Cycles of matter and energy)
Origin and Dispersion of Elements
Particel Acceleration
Planet Formation
Stellar Magnetic Fields

17. Black Hole Spin & Growth
Non-spinning
Rapidly-spinning
Simulation redone by Laura Brenneman, 300 ksec on MGC like AGN. Note that this source is only moderately above average in overall flux, its iron line is one of the strongest available. To get Order(100) such sources, we will go down an order of magnitude in iron line flux – however, the 300 ksec shown here is extreme overkill to show the overall effect. An adequate measurement could be done in ksec. On average, expect 50 ksec observations of sources to get spin distribution (5-10 Msec). a=0.93 is the expected maximum spin value, based on theoretical calculations involving the drag of the disk on the BH; 0.7 is an intermediate value, and a=0 is the non-spinning case.
IXO will measure relativistically-broadened iron line emission, measuring the black hole’s spin.

18. Determining M,R separately
IXO XMS spectrum of
x-ray burst
Slowly rotating (45 Hz), 1.4 M neutron star
Fe XXVI Ha for zGR = 0.35 – determines M/R
Doppler shifts cause line splitting – width depends on R
120s exposure for 1 Crab burst
Can determine M and R via spectral signatures due to pressure broadening, relativistic kinematics (rotation, Doppler shift, time dilation, beaming), and general relativity (light bending around the star, gravitational redshift, frame dragging).
Simulation of what we would see with IXO for these line shapes, during a burst, and including the fact that during the rise of the burst the emission is not uniform but starts at a particular hot spot often thought to be near the pole, and
Then spreads around into a band before enveloping the entire star. Here we see that the difference between R=11.5 and R=9 is easily detected..
Note the exposure time – 120s. The IXO provides such a large increase in area for high resolution spectroscopy
That we can do this quickly, for a large number of NS, which may well cover a large range of mass.
For more rapidly spinning bursting neutron stars IXO High Time Resolution Spectrometer using out-of-focus Silicon Drift Diodes can handle count rates as high as 10^6 per sec with 10's of microsec timing capability. 18

19. Neutron Star Equation of State
Insufficient time to discuss any or all of the models which predict various tracks for NS mass vs radius, nor time to discuss the regions of the plane already constrained by GR, causality, etc
Since accreting NS can provide a range of NS mass, envision just 3 IXO measurements (red ellipses) of ns masses and radii with ~10% precision as shown in the slide. Potential is very high to discriminate among the competing models and extend QCD with confidence to super high density regime.
Lattimer & Prakash 2007

20. TES microcalorimeter

21. Manufacturing and testing
TES on silicon membrane with Pulsed Laser deposition +deep RIE
- Ir/Au, Ti/Au or Mo/Au (total thickness about 100 nm) onto SiN (1 um) suspended membrane
- Absorber (Au, Au/Bi, Cu/Bi, Sn, few um thick) growth on the TES substrate
- Pixel about 250x250 um
Manufacturing facility at INFN Genova
Cryo testing facility at IASF-Roma
Cryo system based on liquid-free Pulse –tube + ADR down to 50 mm (as in-flight)

22. Detector Sizes and Single Pixel results
Ferrari, Gatti et al.
INFN and Genova Univ.
EFWHM = 3.6 eV
INFN and Genova Univ.
Bandler et al., J Low Temp Phys, 151, (2008)
TMU-ISAS
Akamatsu, LTD13, in press, (2009)
Hoevers et al., J Low Temp Phys, 151, (2008)
SRON

23. TES microcalorimeter as flight instrument
Goal: kpixel array with 2 eV resolution
Italy: consortium led by IASF-RM/INAF and INFN/Univ. Genova, IFN-RM/CNR, INAF-Pa, TAS-Mi
Co-Piship for IXO instrument in International Consortium with SRON, Goddard/NASA, JAXA

24. (bond pads for 256 channels only)
TES Arrays
Multiplexing technique is necessary to minimize the heat load caused by thermal conduction through the harness to the cold finger (thousand wires). The array is powered and read by rows or by columns using different Multiplexing methods:
FDM (sinusoidal excitation)
TDM (switch ON/OFF line by line)
CDM (inversion bias polarity)
32x32 NASA GSFC – IXO/XMS
(bond pads for 256 channels only)
Eckart, Doriese, SPIE Newsroom , 2009
FDM technique:
Pixels are AC-biased (line by line)
Summing node (column by column)
De-modulation by the same frequency
to recover the pulse

25. Summary
Future X-ray missions (IXO,Xenia) based on new generation of Transition Edge Sensor microcalorimeters (<2 eV resolution, high count rate capabilities, imaging) enabling spatially resolved high spectral resolution
Fundamental issues addressing cosmology in X-rays and extreme physics